This idea is nothing new at all, consider the topic a lightning rod for brainstorming fun in regards to all of this

Now, I want to go a little feasible here so if we're going to bring up crossbreeds, let's keep the pokemon within the same breeding group. Maybe perhaps within the same first stage while any differences in later stages become apparent there only.

I haven't really seen any of these before, and I think they are all very cool. Some are definitely a stretch, even with breeding groups being the basis, but I do like that you have a standard of reason.

Mudkip+Surskit, for example, is a bit extreme of a cross. Still a cool looking design, even for the ones that I think went too far.